I remember this phrase from The Right Stuff (book and movie) where, as I recall, it was either ‘pushing the outside (or the edge?) of the envelope’ which makes a lot more sense than the now universally used ‘pushing the envelope’.
Is the expression from test pilots going faster and faster via Tom Wolfe’s book?
Writers, in parrotting ‘pushing the envelope’, aren’t really thinking the metaphor through as far as I can see.
What do you think?
(Thanks for a great site by the way!)

I don’t think “mass noun” is the best description of what’s going on here, but it’s another example of how British English and American English differ in how they treat groups (especially of people) with names that are singular in form: collective nouns. British English often considers them as grammatically plural, and gives them a plural verb.

“Arsenal are going to win tomorrow.” vs. “Detroit is going to win tomorrow.”

“Scotland Yard are looking for him.” “The FBI is looking for him.”

The alternate meaning of the headline (that the 8th Army is/are pushing bottles up Germans) doesn’t come readily to a US speaker, because “Army” would require “pushes”, not “push” as a verb, as Faldage notes.

Differences between Britspeak and Yankspeak were discussed ad nauseam on the old site, especially back when wordgeek had a habit of making an issue out of common British spellings and expressions that he claimed never to have encountered before. (For that matter, he often made an issue of common American expressions that he claimed never to have encountered before. He was Not From Around Here.)